The present invention relates to an antifoam composition. More particularly, the present invention relates to an antifoam composition that exhibits excellent and long-lasting antifoam performance under strong alkaline conditions.
Diorganopolysiloxane based antifoam compositions exhibit an antifoam activity superior to that of antifoam compositions based on materials other than silicone oils, for example, alcohols, polyesters, mineral oils, vegetable oils, and synthetic oils and do so at smaller quantities of addition. For these reasons they are in wide use for breaking and suppressing foam in industries such as the chemical industry, food industry, petroleum industry, textile industry, plastics industry, cement industry, and paint and adhesives industry. However, like antifoam compositions based on material other than silicone oil, under strongly alkaline conditions diorganopolysiloxane-based antifoam compositions exhibit a decline in both the level and persistence of their antifoam activity, which necessitates a continuous or intermittent addition of the antifoam composition.
Numerous antifoam compositions have already been proposed in order to solve this problem. For example, Japanese Patent Application Laid-Open [Kokai or Unexamined] No. 56-48211 [48,211/81] teaches an antifoam composition containing an organopolysiloxane, a polyoxyalkylene-containing organopolysiloxane, silica micropowder, surfactant, and water. Japanese Laid-Open Patent Application Number 59-69110 [69,110/84] teaches an antifoam composition whose base agent is an organopolysiloxane that contains amino-functional organic and oxyalkylene groups. Japanese Patent Publication Number 4-42042 [42,042/92] teaches an antifoam composition containing an organopolysiloxane and silica micropowder whose surface has been treated with a diorganosiloxane oligomer. Japanese Patent Publication Number 4-42043 [42,043/92] teaches an antifoam composition containing an organopolysiloxane, an inorganic ammonium salt compound, and silica micropowder whose surface has been treated with an organosilicon compound. Japanese Laid-Open Patent Application Number 5-184814 [184,814/93] teaches an antifoam composition containing a trimethylsiloxy-terminated dimethylpolysiloxane, a vinyldimethylsiloxy-terminated dimethylpolysiloxane, a dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxysilicate, silica micropowder, and platinum catalyst.
However, under strongly alkaline conditions these antifoam compositions exhibit an unsatisfactory antifoam activity and also a reduced persistence in antifoam activity due in each case to scission under these conditions of the main chain of the organopolysiloxane base agent in such compositions.